Fluoro tolans and liquid crystalline media

ABSTRACT

PCT No. PCT/EP92/00736 Sec. 371 Date Jun. 3, 1992 Sec. 102(e) Date Jun. 3, 1992 PCT Filed Apr. 2, 1992 PCT Pub. No. WO92/18448 PCT Pub. Date Oct. 29, 1992.Fluoro tolans of the formula I    &lt;IMAGE&gt;  I  wherein R1 denotes alkyl with up to 12 carbon atoms wherein one or two non-adjacent CH2 groups may also be replaced by -O-, -O-CO-, -CO-O- and/or -CH=CH-, A is trans-1,4-cyclohexylene or 1,4-phenylene, r is 0 or 1, s is 0 or 1, Q is -CF2- or -OCF2- and - if Y=F and/or L1=L2=F - also a single bond, L1 and L2 are H or F, and Y is H, F or Cl are suitable as components of liquid crystalline media.

The invention relates to fluoro tolans of the formula I ##STR2## whereinR¹ denotes alkyl with up to 12 carbon atoms wherein one or twonon-adjacent CH₂ groups may also be replaced by --O--, --O--CO--,--CO--O-- and/or --CH═CH--,

A is trans-1,4-cyclohexylene or 1,4-phenylene,

r is 0 or 1,

s is 0 or 1,

Q is --CF₂ -- or --OCF₂ -- and -- if Y=F and/or L¹ =L² =F - also asingle bond,

L¹ and L² are H or F, and

Y is H, F or Cl and also to liquid crystalline media being a mixture ofat least 2 compounds characterized in that at least one compound is afluoro tolane according to the formula I.

The compounds of the formula I can be used as components of liquidcrystal media, in particular for displays which are based on theprinciple of the twisted nematic cell, including TN cells with a highertwist angle like STN, SBE, OMI etc., on the guest-host effect, on theeffect of deformation of orientated phases or on the effect of dynamicscattering.

Similar halo tolans without lateral fluorine are described for examplein GB 21 55 465.

Similar halo tolans are also disclosed in EP 02 76 067 and J6 26031.However, there are no examples in these application for compoundsaccording to the invention.

Chloroalkoxy tolans are known from J. Malthete et al., Mol. Crys. Liq.Crys. 23, pp. 233 (1973). There is no hint at tolans as claimed in thepresent application.

The invention was based on the object of discovering new stable liquidcrystal or mesogenic compounds which are suitable as components ofliquid crystalline media and, in particular, have advantageous valuesfor optical and dielectric anisotropy combined with low viscosity andhigh nematogenity.

It has now been found that the compounds of the formula I are highlysuitable as polar components of liquid crystalline media. In particular,they have especially advantageous values of optical and dielectricanisotropy. It is also possible to obtain stable liquid crystal mediawith a broad nematic mesophase range including a good deep temperaturebehavior, a high resistivity and a comparatively low viscosity with theaid of these compounds.

By providing the compounds of the foumula I, the range of liquid crystalsubstances which are suitable under various technological aspects forthe preparation of nematic mixtures is also quite generally widenedconsiderably.

The compounds of the formula I can be used as the base materials fromwhich liquid crystal media are predominantly composed; however, they arepreferably added to liquid crystal base materials of other classes ofcompounds, for example in order to influence the dielectric and/oroptical anisotropy and/or the viscosity and/or the nematic mesophaserange of such a dielectric.

The compounds of the formula I are colourless in the pure state and formliquid crystal mesophases in a temperature range which is favorablyplaced for electrooptical use. They are very stable towards chemicals,heat and light.

The invention thus relates to the compounds of the formula I and the useof these compounds as components of liquid crystal media. The inventionfurthermore relates to liquid crystal media with at least two liquidcrystalline components, wherein at least one component is a compound ofthe formula I and to liquid crystal display elements, in particularelectrooptical display elements, which contain media of this type.

Above and below R¹, A, r, s, Q, Y, L¹ and L² have the meaning givenunless expressly stated otherwise.

The compounds of the formula I accordingly include the preferred tolansof the formula Ia to Ii, wherein Cyc is trans-1,4-cyclohexylene, Phe is1,4-phenylene, PheF is ##STR3## and PheFF ##STR4##

    R.sup.1 -PheF-C.tbd.C-Ph-Q-Y                               Ia

    R.sup.1 -PheF-C.tbd.C-PheF-Q-Y                             Ib

    R.sup.1 -PheF-C.tbd.C-PheFF-Q-Y                            Ic

    R.sup.1 -Cyc-PheF-C.tbd.C-Ph-Q-Y                           Id

    R.sup.1 -Cyc-PheF-C.tbd.C-PheF-Q-Y                         Ie

    R.sup.1 -Cyc-PheF-C.tbd.C-PheFF-Q-Y                        If

    R.sup.1 -Cyc-CH.sub.2 CH.sub.2 -PheF-C.tbd.C-Ph-Q-Y        Ig

    R.sup.1 -Cyc-CH.sub.2 CH.sub.2 -PheF-C.tbd.C-PheF-Q-Y      Ih

    R.sup.1 -Cyc-CH.sub.2 CH.sub.2 -PheF-C.tbd.C-PheFF-Q-Y     Ii

R¹ is preferably alkyl, alkoxy, oxaalkyl or alkenyl and can exhibit astraight-chain or branched structure. Especially preferred are compoundsof subformula Ig (Q-Y is preferably OCF₃, OCHF₂ or Cl) and of subformulaIh (Q-Y is preferably OCF₃, OCHF₂, F or Cl).

Alkyl or alkoxy preferably are straight-chain and have 2, 3, 4, 5, 6 or7 C atoms. Accordingly they are preferably ethyl, propyl, butyl, pentyl,hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy or heptoxy, alsomethyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl, methoxy, octoxy, nonoxy, decoxy, undecoxy, dodecoxy,tridecoxy or tetradecoxy.

Oxaalkyl is preferably straight-chain 2-oxapropyl (=methoxymethyl),2-(=ethoxymethyl) or 3-oxybutyl (=2-methoxyethyl), 2-, 3- or4-oxapentyl, 2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-5- or 6-oxaheptyl, 2-,3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or2-, 3-, 4-, 5-, 6-, 7-, 8-, or 9-oxadecyl.

Alkenyl is preferably straight-chain and has 2 or 10 C atoms. It isaccordingly, in particular, vinyl, prop-1- or prop-2-enyl, but-1-, -2-or -3-enyl, pent-1-, -2-, -3-or -4-enyl, hex-1-, -2-, -3-, -4- or-5-enyl, hept-1-, -2-, -3-, -4-, -5-or -6-enyl, oct-1-, -2-, -3-, -4-,-5- -6- or -7-enyl, non-1-, -2-, -3-, -4-, -5-, -6-, -7-or -8-enyl ordec-1-, -2-, -3-, -4-, -5-, -6-, -7-, -8- or -9-enyl.

Compounds of the formula I containing a branched terminal group canoccasionally be of importance because of an improved solubility in thecustomary liquid crystal base materials, but in particular as chiraldoping substances if they are optically active. Branched groups of thistype as a rule contain not more than one chain branching. Preferredbranched radicals are isopropyl, 2-butyl (=1-methylpropyl), isobutyl(=2-methylpropyl, 2-methylbutyl, isopentyl, (=3-methylbutyl),2-methylpentyl, 2-ethylhexyl, 2-propylpentyl, 2-octyl, isopropoxy,2-methylpropoxy, 2-methylbutoxy, 3-methylbutoxy, 2-methylpentoxy,3-methylpentoxy, 2-ethylhexoxy, 2-methylhexoxy, 1-methylhexoxy,1-methylheptoxy (=2-octyloxy), 2-oxa-3-methylbutyl,3-oxa-4-methylpentyl, 4-methylhexyl, 2-nonyl, 2-decyl, 2-dodecyl,6-methyloctoxy, oxy, 2-methyl-3-oxapentyl and 2-methyl-3-oxahexyl.

In the case of compounds with a branched terminal group R¹, formula Iincludes both the optical antipodes and racemates as well as mixturesthereof.

A is preferably trans-1,4-cyclohexylene. L¹ is preferably H and L² ispreferably F. Also preferred are tolans wherein L¹ and L² denote F. IfQ-Y=F or if Q=CF₂ or OCF₂ also those tolans are preferred wherein L¹ andL² are hydrogen.

Of the compounds of the formula I and subformulae thereof, those inwhich at least one of the radicals contained therein has one of thepreferred meanings given are preferred.

The compounds of the formula I are prepared by methods which are knownper se, such as are described in the literature (for example in thestandard works, such as Houben-Weyl, Methoden der Organischen ChemieMethods of Organic Chemistry, Georg Thieme Verlag, Stuttgart), and inparticular under reaction conditions which are known and suitable forthe reactions mentioned. Variants which are known per se and are notmentioned in more detail here can also be used in this connection.

If desired, the starting materials can also be formed in situ, such thatthey are not isolated from the reaction mixture but are immediatelyreacted further to give the compounds of the formula I.

The compounds of the formula I can thus be prepared by brominating thecorresponding stilbenes and subsequently subjecting them to adehydrohalogenation. Variants of this reaction which can be used areknown per se and are not mentioned in detail here.

The stilbenes can be prepared by reacting a 4-substituted benzaldehydewith a corresponding phosphorous ylide according to Wittig or byreacting a 4-substituted phenylethylene with a correspondingbromobenzene derivative according to Heck. A further possibility offorming the C.tbd.C triple bond consists in reacting a compound whichcorresponds to the formula I except that it contains a --CH₂ --CO--group in place of the --C.tbd.C-bond, either with an inorganic acidchloride and dehydrohalogenating the --CH₂ --CCl₂ -- group then formedin the presence of a base, or reacting the compound with semicarbazideand selenium dioxide and subsequently converting it into the triple bondby heating in the presence of methyllithium.

It is also possible to convert a corresponding benzil derivative intothe tolane using hydrazine and subsequently HgO.

Compounds of the formula I can also be prepared by coupling alkynyl-zinccompounds with arylhalides analogously to the process described by A. O.King, E. Negishi, F. J. Villani and A. Silveira in J. Org. Chem. 43(1978) 358.

Compounds of the formula I can also be prepared by theFritsch-Buttenberg-Wiechell rearrangement (Ann. 279, 319, 327, 332,1894) in which 1,1-diaryl-2-halogenoethylenes are rearranged in thepresence of strong bases to form diarylacetylenes.

Preferably, compounds of the formula I are prepared from 4-substitutedphenylacetylenes and aryl halides in the presence of a palladiumcatalyst, for example bis-(triphenylphosphine)-palladium(II) chlorideand copper(I) iodide (described in Synthesis (1980) 627 or TetrahedronLetters 27 (1986) 1171).

Other routes are apparent to the skilled worker. All these steps and thecorresponding reaction conditions are known to the skilled worker.

In addition to one or more compounds for formula I the liquid crystalmedia according to the invention preferably contain 2-40 components andin particular 4-30 components. Liquid crystal media being composed ofone or more compounds of formula I and 7-25 other components areespecially preferred.

These additional components are preferably chosen from the nematic ornematogenic (monotropic or isotropic) substances; in particular from theclasses of azoxybenzenes, benzylideneanilines, biphenyls, terphenyls,phenyl or cyclohexyl benzoates, phenyl or cyclohexylcyclohexanecarboxylates, phenyl or cyclohexyl cyclohexylbenzoates,phenyl or cyclohexyl cyclohexylcyclohexanecarboxylates,cyclohexylphenylbenzoates, cyclohexylphenyl cyclohexanecarboxylates,cyclohexylphenyl cyclohexylcyclohexanecarboxylates, phenylcyclohexanes,cyclohexylbiphenyls, phenylcyclohexylcyclohexanes,cyclohexylcyclohexanes, cyclohexylcyclohexenes,cyclohexylcyclohexylcyclohexene, 1,4-bis-cyclohexylbenzenes,4,4'-bis-cyclohexylbiphenyls, phenyl- or cyclohexylpyrimidines, phenyl-or cyclohexylpyridines, phenyl- or cyclohexyldioxanes, phenyl-orcyclohexyl-1,3-dithianes, 1,2-diphenylethanes, 1,2-dicyclohexylethanes,1-phenyl-2-cyclohexylethanes,1-cyclohexyl-2-(4-phenyl-cyclohexyl)-ethanes,1-cyclohexyl-2-biphenylethanes, 1-phenyl-2-cyclohexyl-phenylethanes,optionally halogenated stilbenes, benzyl phenyl ethers, tolans andsubstituted cinnamic acids.

The 1,4-phenylene groups of these compounds may be fluorinated.

The most important compounds which are possible constituents of liquidcrystal media according to the invention can be characterized by theformalae 1, 2, 3, 4 and 5:

    R'-L-U-R"                                                  1

    R'-L-COO-U-R"                                              2

    R'-L-OOC-U-R"                                              3

    R'-L-CH.sub.2 CH.sub.2 -U-R"                               4

    R'-L-C.tbd.C-U-R"                                          5

In the formulae 1, 2, 3, 4 and 5 L and U may be equal or different fromeach other. L and U independently from each other denote a bivalentresidue selected from the group consisting of --Phe--, --Cyc--,--Phe--Phe--, --Phe--Cyc--, --Cyc--Cyc--, --Pyr--, --Dio--, --G--Phe--,--G--Cyc-- and their mirror images; in this compilation of residues Phedenotes unsubstituted or fluorinated 1,4-phenylen, Cyc trans-1,4-cyclohexylene or 1,4-cyclohexenylen, Pyr pyrimidine-2,5-diyl orpyridine-2,5-diyl, Dio 1,3-dioxane-2,5-diyl and G2-(trans-1,4-cyclohexyl)-ethyl, pyrimidine-2,5-diyl, pyridine-2,5-diylor 1,3-dioxane-2,5-diyl.

One of the residues L and U is preferably Cyc, Phe or Pyr. U preferablydenotes Cyc, Phe or Phe-Cyc. The liquid crystal media according to theinvention preferably contain one or more components selected from thecompounds of formulae 1, 2, 3, 4 and 5 with L and U meaning Cyc, Phe andPyr, said liquid crystal media further containing at the same time oneore more components selected from the compounds of formulae 1, 2, 3, 4and 5 with one of the residues L and U denoting Cyc, Phe and Pyr and theother residue being selected from the group consisting of --Phe--Phe--,--Phe--Cyc--, --Cyc--Cyc--, --G--Cyc--, said liquid crystal mediacontaining in addition to this optionally one or more componentsselected from the compounds of formulae 1, 2, 3, 4 and 5 with L and Ubeing selected from the group consisting of --Phe--Cyc--, --Cyc--Cyc--,--G--Phe-- and --G--Cyc.

In a preferred subgroup of the compounds of formulae 1, 2, 3, 4 and 5(subgroup 1) R' and R" are independently from each other alkyl, alkenyl,alkoxy, alkenoxy with up to 8 carbon atoms. R' and R" differ from oneanother in most of these compounds, one of the residues usually beingalkyl or alkenyl. In another preferred subgroup of the compounds offormulae 1, 2, 3, 4 and 5 (subgroup 2) R" denotes --CN, --CF₃, --OCF₃,--OCHF₂, --F, --Cl or --NCS while R' has the meaning indicated insubgroup 1 and is preferably alkyl or alkenyl. Other variants of theenvisaged substituents in the compounds of formulae 1, 2, 3, 4 and 5 arealso customary. Many such substances are commercially available. Allthese substances are obtainable by methods which are known from theliterature or by analogous methods.

The liquid crystal media according to the invention preferably containin addition to components selected from subgroup 1 also components ofsubgroup 2, the percentage of these components being as follows:

subgroup 1:20 to 90%, in particular 30 to 90%

subgroup 2:10 to 50%, in particular 10 to 50%

In these liquid crystal media the percentages of the compounds accordingto the invention and the compounds of subgroup 1 and 2 may add up togive 100%.

The media according to the invention preferably contain 1 to 40%, inparticular 5 to 30% of the compounds according to the invention. Mediacontaining more than 40%, in particular 45 to 90% of the compoundsaccording to the invention are further preferred. The media containpreferably 3, 4 or 5 compounds according to the invention. The mediaaccording to the invention are prepared in a manner which is customaryper se. As a rule, the components are dissolved in one another,advantageously at elevated temperature. The liquid crystal mediaaccording to the invention can be modified by suitable additives so thatthey can be used in all the types of liquid crystal display devices.Such additives are known to the expert and are described in detail inthe literature (H. Kelker/R. Hatz, Handbook of Liquid Crystals, VerlagChemie, Weinheim, 1980). For example, it is possible to add pleochroicdyestuffs to prepare colored guest-host systems or substances formodifying the dielectric anisotropy, the viscosity and/or theorientation of the nematic phases.

The following examples are to be construed as merely illustrative andnot limitative. m.p.=melting point, c.p.=clearing point. In theforegoing and in the following all parts and percentages are by weightand the temperatures are set forth in degrees Celsius. "Customarywork-up" means that water is added, the mixture is extracted withmethylene chloride, the organic phase is separated off, dried andevaporated, and the product is purified by crystallization and/orchromatography.

Further are:

C: crystalline-solid state, S: smectic phase (the index denoting the typof smectic phase), N: nematic phase, Ch: cholesteric phase, I: isotropicphase. The number being embraced by 2 of these symbols denotes thetemperature of phase change.

EXAMPLE 1

a) A mixture of 0.1 mol of 4-pentyl-2-fluoro-iodobenzene, 0.12 mol oftrimethylsilylacetylene, 0.0014 mol ofbis(triphenylphosphine)-palladium(II) chloride Pd(PPh₃)₂ Cl₂ and 0.7mmol of copper (I) iodide in 250 ml diethylamine is stirred at roomtemperature for 20 hours. After evaporation of the solvent the crudeproduct is purified by chromatography on alumina (4:1petrol/difluoromethane) to give2-(4-pentylphenyl)-1-trimethylsilylacetylene. Removal of thetrimethylsilylgroup is accomplished by treatment this acetylene inmethanol with 1M KOH for 1 hour at room temperature. Evaporation of themethanol and either extraction yields 4-pentyl-2-fluoro-phenylacetylene.

b) 0.2 mmol of Pd(PPh₃)₂ Cl₂ and 0.1 mmol of CuI are added to a mixtureof 0.01 mol of 4-pentylphenylacetylene, 0.01 mol of3,4-difluoro-iodobenzene and 40 ml of diethylamine at room temperatureand stirred for 12 hours. After completion of the reaction, thesuspension is filtered, and the filtrate is concentrated by evaporation.Purification by chromatography and/or crystallization gives4-pentyl-2-fluoro-3',4'-difluoro tolan.

The following are prepared analogously (R¹ =straight-chained alkyl withn carbon atoms):

    ______________________________________                                        n   A      r     s    L1  L2   Q     Y                                        ______________________________________                                        3   --     0     0    H   H    OCF.sub.2                                                                           H                                        3   --     0     0    H   H    OCF.sub.2                                                                           F                                        3   --     0     0    H   F    OCF.sub.2                                                                           Cl                                       3   --     0     0    H   F    --    Cl                                       3   --     0     0    F   F    --    Cl                                       3   --     0     0    F   F    --    F                                        3   --     0     0    F   H    --    F                                        3   --     0     0    H   H    --    F                                        5   --     0     0    H   H    OCF.sub.2                                                                           H                                        5   --     0     0    H   H    OCF.sub.2                                                                           F, C 9 I (S.sub.A --17N --8I)            5   --     0     0    H   F    OCF.sub.2                                                                           Cl                                       5   --     0     0    H   F    --    Cl                                       5   --     0     0    F   F    --    Cl                                       5   --     0     0    F   F    --    F                                        5   --     0     0    F   H    --    F                                        5   --     0     0    H   H    --    F, C 17 I (N --20I)                      3   Cyc    0     1    H   H    OCF.sub.2                                                                           H                                        3   Cyc    0     1    H   H    OCF.sub.2                                                                           F                                        3   Cyc    0     1    H   F    OCF.sub.2                                                                           Cl                                       3   Cyc    0     1    H   F    --    Cl                                       3   Cyc    0     1    F   F    --    Cl                                       3   Cyc    0     1    F   F    --    F                                        3   Cyc    0     1    F   H    --    F                                        3   Cyc    0     1    H   H    --    F                                        3   Cyc    1     1    H   H    OCF.sub.2                                                                           H                                        3   Cyc    1     1    H   H    OCF.sub.2                                                                           F                                        3   Cyc    1     1    H   F    OCF.sub.2                                                                           Cl                                       3   Cyc    1     1    H   F    --    Cl                                       3   Cyc    1     1    F   F    --    Cl                                       3   Cyc    1     1    F   F    --    F                                        3   Cyc    1     1    F   H    --    F                                        3   Cyc    1     1    H   H    --    F, C 5 1.1 N 130.9 I                     2   Cyc    0     1    H   H    OCF.sub.2                                                                           H                                        2   Cyc    0     1    H   H    OCF.sub.2                                                                           F                                        2   Cyc    0     1    H   F    OCF.sub.2                                                                           Cl                                       2   Cyc    0     1    H   F    --    Cl                                       2   Cyc    0     1    F   F    --    Cl                                       2   Cyc    0     1    F   F    --    F                                        2   Cyc    0     1    F   H    --    F                                        2   Cyc    0     1    H   H    --    F                                        2   Cyc    1     1    H   H    OCF.sub.2                                                                           H                                        2   Cyc    1     1    H   H    OCF.sub.2                                                                           F                                        2   Cyc    1     1    H   F    OCF.sub.2                                                                           Cl                                       2   Cyc    1     1    H   F    --    Cl                                       2   Cyc    1     1    F   F    --    Cl                                       2   Cyc    1     1    F   F    --    F                                        2   Cyc    1     1    F   H    --    F                                        2   Cyc    1     1    H   H    --    F                                        4   Cyc    0     1    H   H    OCF.sub.2                                                                           H                                        4   Cyc    0     1    H   H    OCF.sub.2                                                                           F                                        4   Cyc    0     1    H   F    OCF.sub.2                                                                           Cl                                       4   Cyc    0     1    H   F    --    Cl                                       4   Cyc    0     1    F   F    --    Cl                                       4   Cyc    0     1    F   F    --    F                                        4   Cyc    0     1    F   H    --    F                                        4   Cyc    0     1    H   H    --    F                                        4   Cyc    1     1    H   H    OCF.sub.2                                                                           H                                        4   Cyc    1     1    H   H    OCF.sub.2                                                                           F                                        4   Cyc    1     1    H   F    OCF.sub.2                                                                           Cl                                       4   Cyc    1     1    H   F    --    Cl                                       4   Cyc    1     1    F   F    --    Cl                                       4   Cyc    1     1    F   F    --    F                                        4   Cyc    1     1    F   H    --    F                                        4   Cyc    1     1    H   H    --    F                                        5   Cyc    0     1    H   H    OCF.sub.2                                                                           H                                        5   Cyc    0     1    H   H    OCF.sub.2                                                                           F                                        5   Cyc    0     1    H   F    OCF.sub.2                                                                           Cl                                       5   Cyc    0     1    H   F    --    Cl                                       5   Cyc    0     1    F   F    --    Cl                                       5   Cyc    0     1    F   F    --    F                                        5   Cyc    0     1    F   H    --    F                                        5   Cyc    0     1    H   H    --    F, C 78.4 N 162.9 I                      5   Cyc    1     1    H   H    OCF.sub.2                                                                           H                                        5   Cyc    1     1    H   H    OCF.sub.2                                                                           F                                        5   Cyc    1     1    H   F    OCF.sub.2                                                                           Cl                                       5   Cyc    1     1    H   F    --    Cl                                       5   Cyc    1     1    F   F    --    Cl                                       5   Cyc    1     1    F   F    --    F                                        5   Cyc    1     1    F   H    --    F                                        5   Cyc    1     1    H   H    --    F                                        3   Phe    0     1    H   H    OCF.sub.2                                                                           H                                        3   Phe    0     1    H   H    OCF.sub.2                                                                           F                                        3   Phe    0     1    H   F    OCF.sub.2                                                                           Cl                                       3   Phe    0     1    H   F    --    Cl                                       3   Phe    0     1    F   F    --    Cl                                       3   Phe    0     1    F   F    --    F                                        3   Phe    0     1    F   H    --    F                                        3   Phe    0     1    H   H    --    F                                        3   Phe    1     1    H   H    OCF.sub.2                                                                           H                                        3   Phe    1     1    H   H    OCF.sub.2                                                                           F                                        3   Phe    1     1    H   F    OCF.sub.2                                                                           Cl                                       3   Phe    1     1    H   F    --    Cl                                       3   Phe    1     1    F   F    --    Cl                                       3   Phe    1     1    F   F    --    F                                        3   Phe    1     1    F   H    --    F                                        3   Phe    1     1    H   H    --    F                                        2   Phe    0     1    H   H    OCF.sub.2                                                                           H                                        2   Phe    0     1    H   H    OCF.sub.2                                                                           F                                        2   Phe    0     1    H   F    OCF.sub.2                                                                           Cl                                       2   Phe    0     1    H   F    --    Cl                                       2   Phe    0     1    F   F    --    Cl                                       2   Phe    0     1    F   F    --    F                                        2   Phe    0     1    F   H    --    F                                        2   Phe    0     1    H   H    --    F                                        2   Phe    1     1    H   H    OCF.sub.2                                                                           H                                        2   Phe    1     1    H   H    OCF.sub.2                                                                           F                                        2   Phe    1     1    H   F    OCF.sub.2                                                                           Cl                                       2   Phe    1     1    H   F    --    Cl                                       2   Phe    1     1    F   F    --    Cl                                       2   Phe    1     1    F   F    --    F                                        2   Phe    1     1    F   H    --    F                                        2   Phe    1     1    H   H    --    F                                        4   Phe    0     1    H   H    OCF.sub.2                                                                           H                                        4   Phe    0     1    H   H    OCF.sub.2                                                                           F                                        4   Phe    0     1    H   F    OCF.sub.2                                                                           Cl                                       4   Phe    0     1    H   F    --    Cl                                       4   Phe    0     1    F   F    --    Cl                                       4   Phe    0     1    F   F    --    F                                        4   Phe    0     1    F   H    --    F                                        4   Phe    0     1    H   H    --    F                                        4   Phe    1     1    H   H    OCF.sub.2                                                                           H                                        4   Phe    1     1    H   H    OCF.sub.2                                                                           F                                        4   Phe    1     1    H   F    OCF.sub.2                                                                           Cl                                       4   Phe    1     1    H   F    --    Cl                                       4   Phe    1     1    F   F    --    Cl                                       4   Phe    1     1    F   F    --    F                                        4   Phe    1     1    F   H    --    F                                        4   Phe    1     1    H   H    --    F                                        5   Phe    0     1    H   H    OCF.sub.2                                                                           H                                        5   Phe    0     1    H   H    OCF.sub.2                                                                           F                                        5   Phe    0     1    H   F    OCF.sub.2                                                                           Cl                                       5   Phe    0     1    H   F    --    Cl                                       5   Phe    0     1    F   F    --    Cl                                       5   Phe    0     1    F   F    --    F                                        5   Phe    0     1    F   H    --    F                                        5   Phe    0     1    H   H    --    F                                        5   Phe    1     1    H   H    OCF.sub.2                                                                           H                                        5   Phe    1     1    H   H    OCF.sub.2                                                                           F                                        5   Phe    1     1    H   F    OCF.sub.2                                                                           Cl                                       5   Phe    1     1    H   F    --    Cl                                       5   Phe    1     1    F   F    --    Cl                                       5   Phe    1     1    F   F    --    F                                        5   Phe    1     1    F   H    --    F                                        5   Phe    1     1    H   H    --    F                                        ______________________________________                                         (-- = single bond)                                                       

EXAMPLE 2

The liquid crystalline media A and B which are composed as follows:

    ______________________________________                                                                 A    B                                               ______________________________________                                        Composition                                                                   (weight %)                                                                     ##STR5##                  10.0   10.0                                         ##STR6##                  24.0   24.0                                         ##STR7##                  5.0    5.0                                          ##STR8##                  19.0   16.0                                         ##STR9##                  6.0    6.0                                          ##STR10##                 6.0    5.0                                          ##STR11##                 5.0    5.0                                          ##STR12##                 6.0    6.0                                          ##STR13##                 6.0    6.0                                          ##STR14##                 4.0    --                                           ##STR15##                 4.0    6.0                                          ##STR16##                 --     5.0                                          ##STR17##                 5.0    6.0                                         ______________________________________                                    

show the following parameters:

    ______________________________________                                                      A       B                                                       ______________________________________                                        S--N [°C.]                                                                             <-40      <-40                                                Clearing point [°C.]                                                                   73        77                                                  Viscosity at 20° C.                                                                    16        16                                                  [mm.sup.2 s.sup.-1 ]                                                          Δn (589 nm, 20° C.)                                                              0.1364    0.1330                                              ______________________________________                                    

EXAMPLE 3

A supertwisted liquid crystal device (240° twist, yellow mode, 1:200duty, 1:15 bias, 128 Hz) based on the mixtures A and B of example 2 anda commercially available dopant S-811 (E. Merck, Darmstadt) is made andtested as follows:

    ______________________________________                                                         A     B                                                      ______________________________________                                        V.sub.10 (Volt)    2.34    2.35                                               V.sub.90 (Volt)    2.44    2.45                                               V.sub.90 /V.sub.10 1.043   1.043                                              (T.sub.on + T.sub.off)/2 (msec)                                                                  201     201                                                ______________________________________                                    

We claim:
 1. Fluoro tolans of the formula I ##STR18## wherein R¹ denotesalkyl with up to 12 carbon atoms wherein one or two non-adjacent CH₂groups may also be replaced by --O--, --O--CO--, --CO--O-- and/or--CH═CH--,A is trans-1,4-cyclohexylene or 1,4-phenylene, r is 0 or 1, sis 0 or 1, Q is --CF₂ --, --OCF₂ -- or a single bond, L¹ is H, L² is Hor F, and Y is F.
 2. Fluoro tolans of claim 1, wherein L¹ is H and L² isF.
 3. Fluoro tolans of claim 1, wherein L¹ =L² =H, Q=--OCF₂ and R¹ isalkyl having 2 to 12 carbon atoms.
 4. Fluoro tolans of claim 1, whereins is 0 and R¹ is an alkyl group with up to 10 carbon atoms.
 5. Fluorotolans of claim 1, wherein s is 1, r is 0 and A istrans-1,4-cyclohexylene.
 6. Fluoro tolans of claim 1, wherein s and rare 1 and A is trans-1,4-cyclohexylene.
 7. Liquid crystalline mediumbeing a mixture of at least two compounds, characterized in that atleast one compound is a fluoro tolan according to claim
 1. 8. Liquidcrystal display device, characterized in that it contains a liquidcrystalline medium according to claim
 7. 9. Electrooptical displaydevice, characterized in that it contains a liquid crystalline mediumaccording to claim
 7. 10. Fluoro tolans of the formula I ##STR19##wherein R¹ denotes alkyl with up to 12 carbon atoms wherein one or twonon-adjacent CH₂ groups may also be replaced by --O--, --O--CO--,--CO--O-- and/or --CH═CH--,A is trans-1,4-cyclohexylene or1,4-phenylene, r is 0 or 1, s is 0 or 1, Q is --CF₂ --, --OCF₂ -- or asingle bond, L¹ is H, L² is H, and Y is F.